The present invention relates generally to a method of growing crystalline ingots and, more particularly, to a method of growing large-diameter, substantially dislocation-free crystalline ingots having a  less than 110 greater than  crystal direction.
The monocrystalline silicon that is the starting material for many semiconductor electronic components is commonly prepared by a Czochralski (xe2x80x9cCZxe2x80x9d) process. In this process, pieces of polycrystalline silicon are placed in a crucible and melted to a liquidous state, thereby creating a melt. A seed crystal having the desired monocrystalline atomic structure is then lowered into contact with the molten silicon. As the seed crystal is slowly extracted from the melt, a monocrystalline ingot is drawn from the melt having the same atomic structure as the seed crystal.
Unfortunately, dislocation defects are generated in the seed crystal due to the thermal shock created as the seed crystal contacts the melt. Unless corrective actions are taken, the dislocation defects can propagate through and multiply in the growing crystal. As known to those skilled in the art, dislocations generally propagate along crystallographic planes. For a silicon seed crystal having a  less than 100 greater than  crystal direction, the dislocations typically propagate along a plane that extends at an angle of 55xc2x0 from the longitudinal axis of the crystal. For a silicon seed crystal having a  less than 110 greater than  crystal direction, the dislocations typically propagate along a plane that extends at an angle of 54.74xc2x0 from the longitudinal axis of the crystal or propagate along the growth axis itself.
In order to terminate the dislocations prior to propagation through the main body of the crystalline ingot, crystals are typically grown with a neck section extending between the seed crystal and the main body of the crystal. The most common method of eliminating dislocations is known as the Dash method and involves growing a neck having a relatively small diameter and a relatively long length. For example, for a crystalline ingot having a  less than 100 greater than  crystal direction, a neck grown according to the Dash method may have a diameter of between 2 mm and 4 mm and a length between 30 mm and 200 mm. As the neck is grown, the dislocations propagate through the neck toward the interface of the seed crystal and the melt. As a result of the extended length and small diameter of the neck, however, the dislocations terminate at the exterior surface of the neck such that the main body of the crystal is dislocation free (xe2x80x9cDFxe2x80x9d). The crystal is then expanded in diameter through the shoulder or cone portion to the DF main body. Since there is no easy and reliable method to determine if the dislocations have been terminated, the Dash method generally requires the neck to have a relatively small diameter and an extended length in order to effectively terminate most, if not all, dislocations.
Although the Dash method is widely utilized to grow large-diameter crystalline ingots having a  less than 100 greater than  orientation, including ingots having diameters exceeding 200 mm, the growth of large-diameter DF crystalline ingots having a  less than 110 greater than  orientation has been limited to ingots having a diameter of less than approximately 155 mm. Crystals having a  less than 110 greater than  orientation are more difficult to grow than crystals having a  less than 100 greater than  orientation because dislocations in  less than 110 greater than  crystals can propagate along the growth axis, resulting in a crystal having no usable material. In addition, the thin neck grown according to the Dash method limits the crystal length and weight.
DF crystalline ingots having a  less than 110 greater than  orientation are particularly desirous because such ingots have an improved wafer oxidation rate over crystalline ingots having a  less than 100 greater than  orientation and an improved surface state density and Epi-pattern displacement over crystalline ingots having a  less than 100 greater than  orientation. Thus, a need exists for an improved technique for growing large-diameter DF crystalline ingots having a  less than 110 greater than  crystal direction and, in particular, a technique for growing DF crystalline ingots having a  less than 110 greater than  crystal direction and a diameter of approximately 200 mm and larger.
The present invention provides a DF crystalline ingot having a  less than 110 greater than  crystal direction and a diameter of at least about 200 mm and an associated method of manufacture. More specifically, the present invention provides a monocrystalline ingot formed of silicon in which the crystalline ingot has a  less than 110 greater than  crystal direction and a diameter of at least about 200 mm. In one embodiment, the crystalline ingot is doped with phosphorous, arsenic, antimony, boron, aluminum, gallium, or indium. In another embodiment, the crystalline ingot includes a body portion and a neck extending therefrom. Advantageously, at least a portion of the neck adjacent to the body portion has a recurring hourglass configuration to thereby facilitate termination of dislocations within the neck. The portion of the neck defining the recurring hourglass configuration preferably has a diameter alternating between about 2 mm and about 2.5 mm.
The present invention also provides a method of manufacturing a DF crystalline ingot, including providing a liquidous melt. In one embodiment, a seed crystal having a  less than 110 greater than  crystal direction and a length of about 100 mm to about 120 mm is provided. In another embodiment, a seed crystal having a  less than 110 greater than  crystal direction and a width of about 15 mm is provided. Next, the seed crystal is contacted with the surface of the melt. In one embodiment, the seed crystal is positioned near the melt prior to the contacting step to thereby raise the temperature of the seed crystal. In another embodiment, the seed crystal is held in contact with the melt after the contacting step until the temperature of the seed crystal stabilizes. In still another embodiment, a portion of the seed crystal is inserted into the melt after the contacting step such that the inserted portion of the seed crystal melts. For example, in one embodiment, a portion of the seed crystal about 1 mm to about 10 mm in length is inserted into the melt.
The seed crystal is then withdrawn from the melt to thereby grow a neck. Thereafter, the neck is withdrawn from the melt to grow a crystalline ingot having a  less than 110 greater than  crystal direction and a diameter of at least about 200 mm. In one embodiment, the seed elevation rate is automatically modified during the first withdrawing step to reduce the diameter of the neck to greater than about 2.5 mm. Thereafter, the seed elevation rate is manually modified to alternate the diameter of the neck between about 2 mm and about 2.5 mm to thereby shape the neck into a recurring hourglass configuration. Advantageously, the portion of the neck having the recurring hourglass configuration facilitates termination of dislocations within the neck such that the crystalline ingot grown during the second withdrawing step is substantially dislocation free. The crystalline ingot preferably includes a shoulder, main body, and an elongate tail portion. In one embodiment, the temperature of the melt is modified during the second withdrawing step to flatten the cone portion of the crystalline ingot.
In another embodiment of the present invention, the seed crystal is withdrawn from the melt to thereby grow a neck having a first portion and a second portion. The first portion of the neck has a diameter that tapers from the diameter of the seed crystal. The second portion of the neck has a diameter alternating between about 2 mm and about 2.5 mm and has a recurring hourglass configuration. Advantageously, substantially all dislocations are terminated within the second portion of the neck. In one embodiment, the seed elevation rate is automatically modified during the withdrawing step to form the first portion of the neck. Thereafter, the seed elevation rate is manually modified to form the second portion of the neck. The second portion of the neck is then withdrawn from the melt to grow a crystalline ingot having a  less than 110 greater than  crystal direction and a diameter of at least about 200 mm.
Accordingly, there has been provided an improved technique for growing large-diameter DF crystalline ingots having a  less than 110 greater than  crystal direction. Advantageously, the technique allows DF crystalline ingots having a  less than 110 greater than  crystal direction and a diameter of at least about 200 mm to be grown.